I have a 2003 dodge ram 2500 hemi. About two weeks ago i removed the cat and put a y-pipe in its place with and electric cutout so i can choose to run it through my flowmaster or run it straight piped. On the post cat sensor i did the nonfouler trick and it has worked fine for the two weeks and about 300 miles. Just today i was rolling down a big hill so i decided to shift it into neutral and it died. It runs fine but when i rev it up and the rpms start falling they will either jus go to 0 and it will die or it will get really low around 400 and it will start sputtering and then come back up to normal. Also my idle rpms were around 700-800 but now they are 500. Any ideas on what is wrong? From what i understand you dont want to mess with the pre cat sensor because it controls the a/f ratio. correct? the y pipe installation was done after the pre cat sensor so it shouldnt effect it. Also a light came on the dash. i looked it up in the manual and it is an emmisions/ engine control light. sorry for all the questions. I am just really frustrated because this is my only vehicle and i need it.

 

bump. Really need help

 

You need to scan the computer for codes. That will tell you what's wrong.

 

I in no way claim to know what I'm talking about but just throwing this out there...
Could be that you don't have enough back pressure when you're in neutral and rev up. Perhaps when you have it in gear and floor it, there is enough going on with a load on the engine that it's not affected. Think of it this way...when you have it in gear and step on it, then take your foot off the pedal the load on the engine with the trans engaged helps to slow the engine down differently then when you just rev up in neutral and let the rpms drop. Could also be that you rev up the RPMs faster in neutral than you would if you were in gear. that instant rev up dumps a lot of fuel into the cylinders and when you take the foot off the pedal the RPMs drop so fast that it almost floods out and with the y-pipe and less back pressure it could further increase the flooding issue.

 

Ok got everything working fine now. It turns out one side of the y pipe came off so i guess all the air getting in was messing with the precat o2 sensor. I still cant belive this but i guess since the rear sensor controls the a/f ratio, it really screwed my gas mileage up. On the ten mile drive to my friends house where i got it welded so it would be air tight i was literally getting gallons per mile. The gas needle was almost touching the peg when i left my house and when i got to my friends house it was almost down to 7/8ths!! Reset the computer, all the lights went off, went to autozone to get it scanned for codes and it didnt show any, and it runs perfectly now so im glad